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The ability to effectively lead an interdisciplinary translational team is a crucial component of team science success. Most KL2 Clinical Scholars have been members of scientific teams, but few have been team science leaders. There is a dearth of literature and outcome measures of effective Team Science Leadership in clinical and translational research. We focused our curriculum to emphasize Team Science Leadership, developed a list of Team Science Leadership competencies for translational investigators using a modified Delphi method, and incorporated the competencies into a quantitative evaluation survey. The survey is completed on entry and annually thereafter by the Scholar; the Scholar’s primary mentor and senior staff who educate and interact with the Scholar rate the Scholar at the end of each year. The program leaders and mentor review the results with each Scholar. The survey scales had high internal consistency and good factor structure. Overall ratings by mentors and senior staff were generally high, but ratings by Scholars tended to be lower, offering opportunities for discussion and career planning. Scholars rated the process favorably. A Team Science Leadership curriculum and periodic survey of attained competencies can inform individual career development and guide team science curriculum development.

OBJECTIVES/GOALS: There is universal recognition of the importance of team science and team leadership. We have developed a semi-quantitative translational science specific team leadership competency assessment tool and have begun implementation studies to assess the impact of personalized feedback on the team science leadership skills of KL2 Clinical Scholars. METHODS/STUDY POPULATION: To create the instrument, we employed a modified Delphi approach by conducting a thorough literature review on Leadership to concretize the relevant constructs, then used these extracted constructs as a springboard for the Rockefeller Team Science Educators (TSE’s) to discuss and refine the leadership domain areas, collectively create domain-specific survey items. Further discussion helped refined the number, grouping, and wording. Scholars also contributed feedback in item development. We piloted the Leadership Survey by having all of the Rockefeller TSEs rate Clinical Scholars, and having each Scholar rate themselves. Each item was answered using a six-point Likert scale where a low score indicated poor expression and a high score represented excellent expression of the specific leadership attribute. RESULTS/ANTICIPATED RESULTS: Incorporation into a REDCap data base made consenting and rating process by TSE’s and the Scholars straightforward. The a priori domains (Foundational Leadership Competencies, Professionalism, Team Building and Team Sustainability, Appropriate Resource Use and Study Execution, and Regulatory Accountability) had high internal validity and good internal factor structure. The congruence between TSE and Scholar self-ratings were uniformly high, and discordance was often a function of “confidence” and “modesty” on the part of the scholar, rather than deficiency. Supporting comments were informative about performance barriers and mechanisms for improvement. Return of results allowed for the exploration of training gaps. Scholars were surveyed to gauge their reaction to the formal feedback. DISCUSSION/SIGNIFICANCE OF IMPACT: This quantification of team science leadership constructs has allowed for A)- the articulation of constructs essential for successful Translational Scientists to acquire during their training, B)- identification of gaps in that training and skill set, and C)- mechanisms for bolstering any identified gaps in these essential leadership constructs. CONFLICT OF INTEREST DESCRIPTION: None

SummaryProtective vaccines elicit high-affinity, neutralizing antibodies by selection of somatically hypermutated B cell antigen receptors (BCR) on immune complexes (ICs). This implicates Fc-Fc receptor (FcR) interactions in affinity maturation, which, in turn, are determined by IgG subclass and Fc glycan composition within ICs. Trivalent influenza virus vaccination elicited regulation of anti-hemagglutinin (HA) IgG subclass and Fc glycans, with abundance of sialylated Fc glycans (sFc) predicting quality of vaccine response. We show that sFcs drive BCR affinity selection by binding the Type-II FcR CD23, thus upregulating the inhibitory FcγRIIB on activated B cells. This elevates the threshold requirement for BCR signaling, resulting in B cell selection for higher affinity BCR. Immunization with sFc HA ICs elicited protective, high-affinity IgGs against the conserved stalk of the HA. These results reveal a novel, endogenous pathway for affinity maturation that can be exploited for eliciting high-affinity, broadly neutralizing antibodies through immunization with sialylated immune complexes.

HIV-1 immunotherapy with a combination of first generation monoclonal antibodies was largely ineffective in pre-clinical and clinical settings and was therefore abandoned1–3. However, recently developed single cell based antibody cloning methods have uncovered a new generation of far more potent broadly neutralizing antibodies (bNAbs) to HIV-14,5. These antibodies can prevent infection and suppress viremia in humanized mice (hu-mice) and nonhuman primates, but their potential for human HIV-1 immunotherapy has not been evaluated6–10. Here we report the results of a first-in-man dose escalation phase 1 clinical trial of 3BNC117, a potent human CD4 binding site antibody11, in uninfected and HIV-1-infected individuals. 3BNC117 infusion was well tolerated and demonstrated favorable pharmacokinetics. A single 30 mg/kg infusion of 3BNC117 reduced the viral load (VL) in HIV-1-infected individuals by 0.8 – 2.5 log10 and viremia remained significantly reduced for 28 days. Emergence of resistant viral strains was variable, with some individuals remaining sensitive to 3BNC117 for a period of 28 days. We conclude that as a single agent 3BNC117 is safe and effective in reducing HIV-1 viremia, and that immunotherapy should be explored as a new modality for HIV-1 prevention, therapy, and cure.

Florian Klein and colleagues report that treating viremic HIV-1-infected individuals with the broadly neutralizing antibody 10-1074 reduced virus levels in blood, but antibody-resistant virus did emerge. Monoclonal antibody 10-1074 targets the V3 glycan supersite on the HIV-1 envelope (Env) protein. It is among the most potent anti-HIV-1 neutralizing antibodies isolated so far. Here we report on its safety and activity in 33 individuals who received a single intravenous infusion of the antibody. 10-1074 was well tolerated and had a half-life of 24.0 d in participants without HIV-1 infection and 12.8 d in individuals with HIV-1 infection. Thirteen individuals with viremia received the highest dose of 30 mg/kg 10-1074. Eleven of these participants were 10-1074-sensitive and showed a rapid decline in viremia by a mean of 1.52 log10 copies/ml. Virologic analysis revealed the emergence of multiple independent 10-1074-resistant viruses in the first weeks after infusion. Emerging escape variants were generally resistant to the related V3-specific antibody PGT121, but remained sensitive to antibodies targeting nonoverlapping epitopes, such as the anti-CD4-binding-site antibodies 3BNC117 and VRC01. The results demonstrate the safety and activity of 10-1074 in humans and support the idea that antibodies targeting the V3 glycan supersite might be useful for the treatment and prevention of HIV-1 infection.

Interruption of combination antiretroviral therapy in HIV-1-infected individuals leads to rapid viral rebound. Here we report the results of a phase IIa open label clinical trial evaluating 3BNC117,a broad and potent neutralizing antibody against the CD4 binding site of the HIV-1 Env protein, during analytical treatment interruption in 13 HIV-1-infected individuals. Participants with 3BNC117-sensitive virus outgrowth cultures were enrolled. Results show that two or four 30 mg kg(-1) 3BNC117 infusions,separated by 3 or 2 weeks, respectively, are generally well tolerated.Infusions are associated with a delay in viral rebound of 5-9 weeks after two infusions, and up to 19 weeks after four infusions, or an average of 6.7 and 9.9 weeks, respectively, compared with 2.6 weeks for historical controls (P < 0.00001). Rebound viruses arise predominantly from a single provirus. In most individuals,emerging viruses show increased resistance, indicating escape.However, 30% of participants remained suppressed until antibody concentrations waned below 20 μg ml(-1), and the viruses emerging in all but one of these individuals showed no apparent resistance to 3BCN117, suggesting failure to escape over a period of 9-19 weeks.We conclude that the administration of 3BNC117 exerts strong selective pressure on HIV-1 emerging from latent reservoirs during analytical treatment interruption in humans.

3BNC117 is a broad and potent anti-HIV-1 neutralizing antibody that targets the CD4 binding site on the viral envelope spike. When administered passively, this antibody can prevent infection in animal models and suppress viremia in HIV-1-infected individuals. Here we report that HIV-1 immunotherapy with a single injection of 3BNC117 impacts host antibody responses in viremic subjects. In comparison to untreated controls that showed little change in their neutralizing activity over a six-month period, 3BNC117 infusion significantly improved neutralizing responses to heterologous tier 2 viruses in nearly all study participants. We conclude that 3BNC117-mediated immunotherapy enhances host humoral immunity to HIV-1.

Adjuvants are critical for the success of vaccines. Agonists of microbial pattern recognition receptors (PRRs) are promising new adjuvant candidates. A mechanism through which adjuvants enhance immune responses is to stimulate innate immunity. We studied the innate immune response in humans to synthetic double-stranded RNA (polyinosinic:polycytidylic acid [poly IC] stabilized with poly-l-lysine [poly ICLC]), an agonist for toll-like receptor (TLR) 3, and the cytosolic RNA helicase MDA-5. Transcriptional analysis of blood samples from eight volunteers, after subcutaneous administration of poly ICLC, showed up-regulation of genes involved in multiple innate immune pathways in all subjects, including interferon (IFN) and inflammasome signaling. Blocking type I IFN receptor ex vivo significantly dampened the response to poly IC. Comparative transcriptional analysis showed that several innate immune pathways were similarly induced in volunteers immunized with the highly efficacious yellow fever vaccine. Therefore, a chemically defined PRR agonist like poly ICLC can be a reliable and authentic microbial mimic for inducing innate immune responses in humans.

Fms-like tyrosine kinase-3 ligand (Flt3L) uniquely binds the Flt3 (CD135) receptor expressed on hematopoietic stem cells (HSCs), early progenitor cells, immature thymocytes and steady-state dendritic cells (DCs) and induces their proliferation, differentiation, development and mobilization in the bone marrow, peripheral blood and lymphoid organs. CDX-301 has an identical amino-acid sequence and comparable biological activity to the previously tested rhuFlt3L, which ceased clinical development over a decade ago. This Phase 1 trial assessed the safety, pharmacokinetic, pharmacodynamic and immunologic profile of CDX-301, explored alternate dosing regimens and examined the impact of rhuFlt3L on key immune cell subsets. Thirty healthy volunteers received CDX-301 (1-75 μg/kg/day) over 5-10 days. One event of Grade 3 community-acquired pneumonia occurred. There were no other infections, dose-limiting toxicities or serious adverse events. CDX-301 resulted in effective peripheral expansion of monocytes, hematopoietic stem and progenitor cells and key subsets of myeloid DCs and plasmacytoid DCs, with no clear effect on regulatory T cells. These data from healthy volunteers support the potential for CDX-301, as monotherapy or in combination with other agents, in various indications including allogeneic HSC transplantation and immunotherapy, but the effects of CDX-301 will need to be investigated in each of these patient populations.

The Liu and Nussenzweig groups identify the immediate precursor of CD1c+ and CD141+ dendritic cells in the circulation of healthy donors. These precursor cells (hpre-cDC) were detectable in cord blood, bone marrow, blood, and peripheral lymphoid organs., Two subsets of conventional dendritic cells (cDCs) with distinct cell surface markers and functions exist in mouse and human. The two subsets of cDCs are specialized antigen-presenting cells that initiate T cell immunity and tolerance. In the mouse, a migratory cDC precursor (pre-CDC) originates from defined progenitors in the bone marrow (BM). Small numbers of short-lived pre-CDCs travel through the blood and replace cDCs in the peripheral organs, maintaining homeostasis of the highly dynamic cDC pool. However, the identity and distribution of the immediate precursor to human cDCs has not been defined. Using a tissue culture system that supports the development of human DCs, we identify a migratory precursor (hpre-CDC) that exists in human cord blood, BM, blood, and peripheral lymphoid organs. hpre-CDCs differ from premonocytes that are restricted to the BM. In contrast to earlier progenitors with greater developmental potential, the hpre-CDC is restricted to producing CD1c+ and CD141+ Clec9a+ cDCs. Studies in human volunteers demonstrate that hpre-CDCs are a dynamic population that increases in response to levels of circulating Flt3L.

Current human immunodeficiency virus (HIV) vaccine approaches emphasize prime boost strategies comprising multiple doses of DNA vaccine and recombinant viral vectors. We are developing a protein-based approach that directly harnesses principles for generating T cell immunity. Vaccine is delivered to maturing dendritic cells in lymphoid tissue by engineering protein antigen into an antibody to DEC-205, a receptor for antigen presentation. Here we characterize the CD4+ T cell immune response to HIV gag and compare efficacy with other vaccine strategies in a single dose. DEC-205–targeted HIV gag p24 or p41 induces stronger CD4+ T cell immunity relative to high doses of gag protein, HIV gag plasmid DNA, or recombinant adenovirus-gag. High frequencies of interferon (IFN)-γ– and interleukin 2–producing CD4+ T cells are elicited, including double cytokine-producing cells. In addition, the response is broad because the primed mice respond to an array of peptides in different major histocompatibility complex haplotypes. Long-lived T cell memory is observed. After subcutaneous vaccination, CD4+ and IFN-γ–dependent protection develops to a challenge with recombinant vaccinia-gag virus at a mucosal surface, the airway. We suggest that a DEC-targeted vaccine, in part because of an unusually strong and protective CD4+ T cell response, will improve vaccine efficacy as a stand-alone approach or with other modalities.

Dengue virus is a single-stranded, enveloped RNA virus that productively infects human dendritic cells (DCs) primarily at the immature stage of their differentiation. We now find that all four serotypes of dengue use DC-SIGN (CD209), a C-type lectin, to infect dendritic cells. THP-1 cells become susceptible to dengue infection after transfection of DC-specific ICAM-3 grabbing nonintegrin (DC-SIGN), or its homologue L-SIGN, whereas the infection of dendritic cells is blocked by anti–DC-SIGN antibodies and not by antibodies to other molecules on these cells. Viruses produced by dendritic cells are infectious for DC-SIGN– and L-SIGN–bearing THP-1 cells and other permissive cell lines. Therefore, DC-SIGN may be considered as a new target for designing therapies that block dengue infection.

Nature 522, 487–491 (2015); doi:10.1038/nature14411 In this Letter, the grant U19AI111825-01 Cooperative Centers on Human Immunology from NIH was erroneously included in the Acknowledgments section; this has been corrected in the online versions of the paper.

Results Study remains blinded. Transient local and systemic reactogenicity occurred, without vaccine-related serious adverse events to date. Gag p24-specific IgG was induced in 9/15 (60%, 9 received vaccine plus adjuvant) volunteers in both low dose and mid dose groups at weeks 4, 8, 12, and 16. IgG titers were higher in the mid dose group and responses persisted for at least 6 months after last low dose immunization. Gag-specific CD4+ T cells were also detected following immunizations. IL-2 and TNF-a were the predominant cytokines. For CD4+ cells producing IL-2 or TNF-a, the response rates ranged from 33 to 46% (5-7/15 volunteers, 9 received vaccine plus adjuvant) and 8 to 40% (1-6/15 volunteers) post-vaccination in the low and mid dose groups respectively. Among positive responders, the median magnitude across visits ranged from 0.09% to 0.23% in the low dose group and from 0.06% to 0.17% in the mid dose group.

Regulatory T cells generated by allostimulation with dendritic cells, transforming growth factor β, and retinoic acid stably express Foxp3 and can suppress even ongoing GVHD in mice., Foxp3+ regulatory T cells (T reg cells) effectively suppress immunity, but it is not determined if antigen-induced T reg cells (iT reg cells) are able to persist under conditions of inflammation and to stably express the transcription factor Foxp3. We used spleen cells to stimulate the mixed leukocyte reaction (MLR) in the presence of transforming growth factor β (TGF-β) and retinoic acid. We found that the CD11chigh dendritic cell fraction was the most potent at inducing high numbers of alloreactive Foxp3+ cells. The induced CD4+CD25+Foxp3+ cells appeared after extensive proliferation. When purified from the MLR, iT reg cells suppressed both primary and secondary MLR in vitro in an antigen-specific manner. After transfer into allogeneic mice, iT reg cells persisted for 6 mo and prevented graft versus host disease (GVHD) caused by co-transferred CD45RBhi T cells. Similar findings were made when iT reg cells were transferred after onset of GVHD. The CNS2 intronic sequence of the Foxp3 gene in the persisting iT reg cells was as demethylated as the corresponding sequence of naturally occurring T reg cells. These results indicate that induced Foxp3+ T reg cells, after proliferating and differentiating into antigen-specific suppressive T cells, can persist for long periods while suppressing a powerful inflammatory disease.

Background: DNA-based vaccines have been safe but weakly immunogenic in humans to date. Methods and Findings: We sought to determine the safety, tolerability, and immunogenicity of ADVAX, a multigenic HIV-1 DNA vaccine candidate, injected intramuscularly by in vivo electroporation (EP) in a Phase-1, double-blind, randomized placebo-controlled trial in healthy volunteers. Eight volunteers each received 0.2 mg, 1 mg, or 4 mg ADVAX or saline placebo via EP, or 4 mg ADVAX via standard intramuscular injection at weeks 0 and 8. A third vaccination was administered to eleven volunteers at week 36. EP was safe, well-tolerated and considered acceptable for a prophylactic vaccine. EP delivery of ADVAX increased the magnitude of HIV-1-specific cell mediated immunity by up to 70-fold over IM injection, as measured by gamma interferon ELISpot. The number of antigens to which the response was detected improved with EP and increasing dosage. Intracellular cytokine staining analysis of ELISpot responders revealed both CD4+ and CD8+ T cell responses, with co-secretion of multiple cytokines. Conclusions: This is the first demonstration in healthy volunteers that EP is safe, tolerable, and effective in improving the magnitude, breadth and durability of cellular immune responses to a DNA vaccine candidate. Trial Registration: ClinicalTrials.gov NCT00545987

Background We conducted a Phase I dose-escalation trial of ADMVA, a Clade-B'/C-based HIV-1 candidate vaccine expressing env, gag, pol, nef, and tat in a modified vaccinia Ankara viral vector. Sequences were derived from a prevalent circulating HIV-1 recombinant form in Yunnan, China, an area of high HIV incidence. The objective was to evaluate the safety and immunogenicity of ADMVA in human volunteers. Methodology/Principal Findings ADMVA or placebo was administered intramuscularly at months 0, 1 and 6 to 50 healthy adult volunteers not at high risk for HIV-1. In each dosage group [1×107 (low), 5×107 (mid), or 2.5×108 pfu (high)] volunteers were randomized in a 3∶1 ratio to receive ADMVA or placebo in a double-blinded design. Subjects were followed for local and systemic reactogenicity, adverse events including cardiac adverse events, and clinical laboratory parameters. Study follow up was 18 months. Humoral immunogenicity was evaluated by anti-gp120 binding ELISA, immunoflourescent staining, and HIV-1 neutralization. Cellular immunogenicity was assessed by a validated IFNγ ELISpot assay and intracellular cytokine staining. Anti-vaccinia binding titers were measured by ELISA. ADMVA was generally well-tolerated, with no vaccine-related serious adverse events or cardiac adverse events. Local or systemic reactogenicity events were reported by 77% and 78% of volunteers, respectively. The majority of events were of mild intensity. The IFNγ ELISpot response rate to any HIV antigen was 0/12 (0%) in the placebo group, 3/12 (25%) in the low dosage group, 6/12 (50%) in the mid dosage group, and 8/13 (62%) in the high dosage group. Responses were often multigenic and occasionally persisted up to one year post vaccination. Antibodies to gp120 were detected in 0/12 (0%), 8/13 (62%), 6/12 (50%) and 10/13 (77%) in the placebo, low, mid, and high dosage groups, respectively. Antibodies persisted up to 12 months after vaccination, with a trend toward agreement with the ability to neutralize HIV-1 SF162 in vitro. Two volunteers mounted antibodies that were able to neutralize clade-matched viruses. Conclusions/Significance ADMVA was well-tolerated and elicited durable humoral and cellular immune responses. Trial Registration Clinicaltrials.gov NCT00252148

Background We conducted a Phase I dose escalation trial of ADVAX, a DNA-based candidate HIV-1 vaccine expressing Clade C/B' env, gag, pol, nef, and tat genes. Sequences were derived from a prevalent circulating recombinant form in Yunnan, China, an area of high HIV-1 incidence. The objective was to evaluate the safety and immunogenicity of ADVAX in human volunteers. Methodology/Principal Findings ADVAX or placebo was administered intramuscularly at months 0, 1 and 3 to 45 healthy volunteers not at high risk for HIV-1. Three dosage levels [0.2 mg (low), 1.0 mg (mid), and 4.0 mg (high)] were tested. Twelve volunteers in each dosage group were assigned to receive ADVAX and three to receive placebo in a double-blind design. Subjects were followed for local and systemic reactogenicity, adverse events, and clinical laboratory parameters. Study follow up was 18 months. Humoral immunogenicity was evaluated by anti-gp120 binding ELISA. Cellular immunogenicity was assessed by a validated IFNγ ELISpot assay and intracellular cytokine staining. ADVAX was safe and well-tolerated, with no vaccine-related serious adverse events. Local and systemic reactogenicity events were reported by 64% and 42% of vaccine recipients, respectively. The majority of events were mild. The IFNγ ELISpot response rates to any HIV antigen were 0/9 (0%) in the placebo group, 3/12 (25%) in the low-dosage group, 4/12 (33%) in the mid-dosage group, and 2/12 (17%) in the high-dosage group. Overall, responses were generally transient and occurred to each gene product, although volunteers responded to single antigens only. Binding antibodies to gp120 were not detected in any volunteers, and HIV seroconversion did not occur. Conclusions/Significance ADVAX delivered intramuscularly is safe, well-tolerated, and elicits modest but transient cellular immune responses. Trial Registration Clinicaltrials.gov NCT00249106

Open Access Oral presentation OA05-01. In vivo electroporation enhances the immunogenicity of ADVAX, a DNA-based HIV-1 vaccine candidate, in healthy volunteers S Vasan*1, A Hurley1, SJ Schlesinger1, D Hannaman2, DF Gardiner1, DP Dugin1, MM Boente-Carrera1, RM Vittorino1, M Caskey1, J Andersen1, Y Huang1, J Cox3, T Tarragona3, DK Gill3, H Cheeseman3, L Clark3, L Dally4, C Smith4, C Schmidt3, H Park3, E Sayeed3, J Gilmour3, P Fast3, R Bernard2 and DD Ho1

Targeting canarypox (CP)-HIV vaccine to dendritic cells (DCs) elicits anti-HIV-1 immune responses in vitro. We conducted a phase I/II clinical trial to evaluate whether adding DC to a CP-HIV vaccine improved virologic control during analytic treatment interruption (ATI) in HIV-1-infected subjects. Twenty-nine subjects on suppressive antiretroviral therapy were randomized to vaccination with autologous DCs infected with CP-HIV + keyhole limpet hemocyanin (KLH) (arm A, n = 14) or CP-HIV + KLH alone (arm B, n = 15). The mean viral load (VL) setpoint during ATI did not differ between subjects in arms A and B. A higher percentage of subjects in the DC group had a VL setpoint

CD4+Th1 type immunity is implicated in resistance to global infectious diseases. To improve the efficacy of T cell immunity induced by human immunodeficiency virus (HIV) vaccines, we are developing a protein-based approach that directly harnesses the function of dendritic cells (DCs) in intact lymphoid tissues. Vaccine proteins are selectively delivered to DCs by antibodies to DEC-205/CD205, a receptor for antigen presentation. We find that polyriboinosinic:polyribocytidylic acid (poly IC) independently serves as an adjuvant to allow a DC-targeted protein to induce protective CD4+T cell responses at a mucosal surface, the airway. After two doses of DEC-targeted, HIV gag p24 along with poly IC, responder CD4+T cells have qualitative features that have been correlated with protective function. The T cells simultaneously make IFN-γ, tumor necrosis factor (TNF)-α, and IL-2, and in high amounts for prolonged periods. The T cells also proliferate and continue to secrete IFN-γ in response to HIV gag p24. The adjuvant role of poly IC requires Toll-like receptor (TLR) 3 and melanoma differentiation-associated gene-5 (MDA5) receptors, but its analog poly IC12U requires only TLR3. We suggest that poly IC be tested as an adjuvant with DC-targeted vaccines to induce numerous multifunctional CD4+Th1 cells with proliferative capacity.

DNA vaccines promote an immune response by providing antigen-encoding DNA to the recipient, but the efficacy of such vaccines needs improving. Many approaches have considerable potential but currently induce relatively weak immune responses despite multiple high doses of DNA vaccine. Here, we asked whether targeting vaccine antigens to DCs would increase the immunity and protection that result from DNA vaccines. To determine this, we generated a DNA vaccine encoding a fusion protein comprised of the vaccine antigen and a single-chain Fv antibody (scFv) specific for the DC-restricted antigen-uptake receptor DEC205. Following vaccination of mice, the vaccine antigen was expressed selectively by DCs, which were required for the increased efficacy of MHC class I and MHC class II antigen presentation relative to a control scFv DNA vaccine. In addition, a DNA vaccine encoding an HIV gag p41-scFv DEC205 fusion protein induced 10-fold higher antibody levels and increased numbers of IFN-gamma-producing CD4+ and CD8+ T cells. After a single i.m. injection of the DNA vaccine encoding an HIV gag p41-scFv DEC205 fusion protein, mice were protected from an airway challenge with a recombinant vaccinia virus expressing the HIV gag p41, even with 1% of the dose of nontargeted DNA vaccine. The efficacy of DNA vaccines therefore may be enhanced by inclusion of sequences such as single-chain antibodies to target the antigen to DCs.

The recent use of multiparametric flow cytometry to monitor T cell immune responses complements traditional assays, such as IFN-gamma ELISPOT, to provide more information on the functional complexity of CD4+ and CD8+ T cell immune responses induced either by natural infection, or by immunization. In this review, we provide a general background on T cell subsets, and describe the cellular immune response during natural HIV-1 infection. We then review T cell responses to current candidate HIV-1 vaccines. Taken together, this helps to formulate our understanding of the immune correlates of protection required for an effective prophylactic HIV-1 vaccine. Finally, we emphasize current dendritic cell based vaccine strategies designed to modulate immunity to establish immune protection against HIV-1.

Niroshana Anandasabapathy, MD, PhD1, Arlene Hurley, ANP, CCRC1, Gaelle Breton, PhD1, Marina Caskey1, Christine Trumpfheller1, Popi Sarma1, James Pring1, Maggie Pack1, Renee Riggs2, Jennifer Green2, Michael Yellin, MD2, Thomas A. Davis, MD2, Tibor Keler, PhD2 and Sarah Schlesinger, MD1 1Laboratory of Cellular Physiology and Immunology, Rockefeller University, New York, NY; 2Celldex Therapeutics, Inc., Needham, MA

Abstract 4124 Fms-like tyrosine kinase-3 ligand (Flt3L) uniquely binds the Flt3 (CD135) receptor expressed on hematopoietic stem cells (HSC), early progenitor cells, immature thymocytes, and steady state dendritic cells and induces the proliferation, differentiation, development and mobilization of these cells in the bone marrow, peripheral blood, and lymphoid organs. Given its potential as a stem cell mobilizer and immunotherapeutic, the safety and biologic activity of recombinant human (rh) Flt3L were originally demonstrated in clinical studies conducted by Immunex Inc, but development had been halted. CDX-301 is a soluble, rhFlt3L composed of the identical amino acid sequence and comparable biologic activity as the Immunex product. A Phase 1 trial was initiated to assess the safety, pharmacokinetic, pharmacodynamic and immunologic profile of CDX-301. Using a standard 3+3 dose-escalating design, 18 healthy volunteers (HV) (51% male, median age = 32 years) received 5 daily subcutaneous injections of CDX-301 (at a dose of 1, 3, 10, 25 or 75 mcg/kg) followed by 28-day observation. All HV completed dosing and CDX-301 was well tolerated. Dose-escalation proceeded through the 25 mcg/kg dose level with no DLT (n=3 in each cohort). In the 75 mcg/kg cohort, one HV with a remote history of community acquired pneumonia developed community acquired pneumonia on study day 12; the event responded rapidly to antibiotic treatment and fully recovered within 2 weeks, but was considered a dose-limiting toxicity given the temporal association with CDX-301 administration. The cohort was expanded to a total of six HV, and no additional infections or DLT were reported. Transient Grade 1 lymphadenopathy was observed in 3 HV across multiple dose levels. No anti-CDX-301 antibodies were detected through end of study day 34 in any HV. White blood cell count (WBC) and monocytes increased in all HV; peak levels were observed around Day 10 and generally returned to baseline by Day 34. At doses above 3 mcg/kg, there was no clear dose response; mean maximum % change from baseline for the HV receiving 10 – 75 mcg/kg = 111% (range: 55–224%) for WBC and 800% (range: 450–1167%) for monocytes. In-depth phenotypic and/or functional analysis of hematopoietic stem cells and dendritic cell subsets are planned. Data from this current Phase 1 trial are consistent with previous studies showing that rhFlt3L can safely and effectively mobilize hematopoietic cell populations. Two additional cohorts will receive extended dosing (25 mcg/kg dose; 7 & 10 day durations) to further define an optimal dosing regimen for planned trials of CDX-301 in allogeneic hematopoietic stem cell transplantation (HSCT) and immunotherapy. Disclosures: Riggs: CelldexTherapeutics: Employment, Equity Ownership. Green:Celldex: Employment, Equity Ownership. Yellin:CelldexTherapeutics: Employment, Equity Ownership. Davis:CelldexTherapeutics: Employment, Equity Ownership. Keler:CelldexTherapeutics: Employment, Equity Ownership.